/Engine/Source/Editor/UnrealEd/Public/Kismet2/BlueprintEditorUtils.h
Find how many actors reference the supplied actor
static void FindActorsThatReferenceActor ( [AActor](API\Runtime\Engine\GameFramework\AActor) * InActor, [TArray](API\Runtime\Core\Containers\TArray)< [UClass](API\Runtime\CoreUObject\UObject\UClass) * > & InClassesToIgnore, [TArray](API\Runtime\Core\Containers\TArray)< [AActor](API\Runtime\Engine\GameFramework\AActor) * > & OutReferencingActors )